After-glow suppressing cellulose derivatives



, 2,990,233 Patented June 27, 1961 2,990,233 AFTER-GLOW SUPPRESSING CELLULOSE DERIVATIVES Eugene Pacsu and Robert F. Schwenker, .ln, Princeton, N..l., assignors to Textile Research Institute, Princeton, N.J., a corporation of New Jersey No Drawing. Filed Dec. 31, 1956, Ser. No. 631,508 6 Claims. (Cl. 8-116) This invention relates to phosphorous containing cellulose derivatives which exhibit no after-glow when burned or charred. The invention further relates to methods of producing new flame resistant cellulose derivatives.

Recent investigations have indicated that the characteristic flammability of cellulose is due, in part, to the initial formation of the ,B-glucose anhydride known as levoglucosan as an intermediate product, which is then decomposed to form flammable decomposition products. In our copending application Serial No. 631,411 filed Dec. 31, 1956 we have described methods and products whereby the formation of levoglucosan on burning of cellulosic materials is reduced or prevented. These results are attained by certain esterification of the cellulose and the introduction of halogen into at least some of the glucose anhydride units.

The flame retarding properties of these new cellulosic derivatives is very satisfactory. However, upon prolonged ignition at least some of these and other cellulose products develop a char or carbonaceous residue which exhibits an objectionable amount of after-glow.

The introduction of phosphorus into the cellulose molecule has been said to increase the flame retarding properties of cellulose derivatives (Malm et al. Patent No. 2,008,986). However, the methods of the proir art involve prolonged phosphorylation treatment at elevated temperatures. Under such conditions, the cellulose is seriously degraded with the result that textile fabrics and other cellulosic materials are so weakened that they have little or no practical value.

It has now been discovered that limited phosphorylation of cellulose can be eifected in a very short period of time and at relatively low temperatures without appreciably degrading the cellulose or altering the physical properties of the material treated. While such limited phosphorylation does not greatly increase the flame retardant properties of the cellulose, it effectively eliminates after-glow.

In accordance with the present invention, the elimination of after-glow in cellulosic materials on burning or charring thereof is effected by limited phosphorylation without impairing the physical properties of the material treated. Flame retardant properties also may be imparted to the material by any desired method including that of our copending application referred to above. By combining the present phosphorylation treatment with other treatments which increase the flame resistant properties of cellulosic materials, it is possible to produce materials having outstanding value capable of meeting the most rigid fire regulations.

The amount of phosphorus which must be introduced into the cellulose in order to suppress after-glow need not exceed about 2% by weight and may be as low as 0.2%, corresponding to the introduction of 1 phosphorus containing group to every 15 to 60 or more glucose anhydride units in the cellulose macro molecule.

The advantages of the present invention are preferably attained by giving the cellulosic material a pretreatment, preferably with an organic sulfonyl chloride,

prior to phosphorylation. In this way the introduction of the phosphorus containing group into the cellulose molecule is facilitated and can be effected readily at relatively low temperatures and in a matter of a few minutes. Degradation of the cellulose is avoided and the process can be carried out in treating fabricated cellulose containing materials such as textile fabrics, including woven and unwoven cotton, and rayon fabrics, paper, cellulose films and the like. However, the process is equally applicable to the treatment of cotton linters, paper making fibers, leaf and bast fibers such as flax, hemp, sisal and the like, as well as mattress filling materials, and substantially any cellulose containing material, including mixtures of fibers in which cotton or viscose rayon is bended with wool, silk or other fibers.

The principal object of the present invention is to provide novel methods for reducing the after-glow of cellulose containing materials on burning or charring thereof.

Another object of the invention is to produce new phosphorus containing cellulose derivatives which are characterized by their desirable physical properties and resistance to after-glow.

A further object of the invention is to provide methods whereby phosphorus may be introduced into the cellulose molecule by a short treatment at relatively low temperatures.

A specific object of the invention is to produce flame resistant cellulose derivatives which exhibit no after-glow by methods in which the cellulose is first treated with an organic sulfonyl chloride and thereafter phosphorylated and reacted with a halide.

These and other objects and features of the invention will appear from the following description thereof in which reference is made to preferred methods and com positions for the purpose of indicating the general nature of the invention but without intending to limit the scope of the invention thereby.

In accordance with the present invention the phosphorus containing agent employed for the treatment of cellulose is a phosphorus compound containing only one halogen atom, the remaining valences of the phosphorus preferably being occupied by oxygen or groups which will not react with the labile hydrogen of the cellulose. Typical of such agents are the dialkyl halophosphates such as diethyl chlorophosphate, diethyl iodophosphate, dibutyl chlorophosphate, and the like. Compounds of this character have only one halogen atom available for reaction with the OH groups of the cellulose and, as a result, cross linkage and material change in the structure of the cellulose itself does not occur.

The phosphorylation of cellulose is preferably carried on in the presence of a tertiary amine such as pyridine, although lutidine, quinoline or other tertiary amines may be used. It is believed that a pyridinium type of complex is formed as the first step in the reaction. Such a reaction may be represented by the following equation The second step of the reaction is believed to involve the substitution of the diethylphosphonyl group for the labile hydrogen in the primary alcohol group to yield a phosphocellulose containing unit of the type I cniororcrnbou 1 11 l o l Ix l 011 /i i OH l l l l 0/ O l on ornon The reaction is evidently facilitated by pretreatment of the cellulose. The preferred pretreatment is of the type described in our copending application referred to above wherein the cellulose is first reacted with an organic sulfonyl chloride to esterify at least some of the hydroxyl groups in the 6 position of the glucose anhydride units of the molecule. However, mercerization of the cellulose prior to phosphorylation is helpful and even the mere wetting out of a fabric by brief immersion in water with subsequent drying appears to aid in carrying out the phosphorylation treatment. The phosphorus containing groups probably enter the molecule at available sites in the 6 position of the glucose anhydride units but they may also replace the labile hydrogens in the 2 or 3 positions of the units.

When the cellulose has been prepared for treatment by reaction with an organic sulfonyl chloride, the phosphorylating reaction may be carried out at room temperatures if desired. However, degradation of the cellulose increases as the temperature is raised and therefore it is ordinarily preferable to carry out the reaction at temperatures below about 40 C. Nevertheless, short treatments at temperatures as high as 100 C. are permissible and the reaction will take place at temperatures as low as 0 C.

The duration of the treatment may be varied depending upon various factors such as the temperature at which the reaction is carried out, the concentration of the reagents employed, the nature and extent of the pretreatment to which the cellulosic material has been subjected, and the degree of phosphorylation desired. Ordinarily treatment for less than 1 hour and preferably for a period of 5 to minutes at room temperature will suffice to effect a degree of phosphorylation of mesylated cellulose sufficient to prevent after-glow in a cellulosic fabric. Longer or shorter periods of treatment, up to several hours or as short as a minute or so, can be employed if desired.

In the preferred treatment, the phosphorylating agent used is diethyl chlorophosphate and is employed in amount corresponding to 3 moles of the phosphorylating agent to 1 mole of cellulose (based on a molecular weight of 162 for the cellulose monomer). This concentration may be varied depending upon the conditions of treatment and the nature and extent of pretreatment of the cellulose. Ordinarily a range in rnole concentration of about 1 to l to 4 to l of the phosphorylating agent to cellulose is preferred, although higher concentrations of the phosphorylating agent may be used if de sired.

Degradation of the cellulose and tenderizing of the material is greater when the product has a high phosphorus content. However, the duration and temperature of the phopshorylating treatment have a much greater effect upon the physical properties of the material than does the ultimate phosphorus content. Thus, products treated for several hours at elevated temperatures may be so weakened as to have but little practical value even though their phosphorus content is less than 1%, whereas products having a higher phosphorus content will be unimpaired in tensile strength if they are treated at room temperature and for a shorter time.

In order to illustrate typical procedures in accordance with the present invention, the following examples are cited.

4 EXAMPLE I Various samples of cotton fabrics were wetted out with water and the excess water was removed by partial drying at 50 C. Some of the samples used were first given a mercerizing treatment for minutes in a aqueous sodium hydroxide solution. Each of the samples after being Wetted out and dried was soaked in pyridine to replace the residual water and then removed to a flask and covered with pyridine. Diethyl chlorophosphate was added to the pyridine in a quantity sufficient to give 3 moles of diethyl chlorophosphate to 1 mole of cellulose (based on a molecular weight of 162 for the cellulose monomer). The reaction was allowed to proceed for various periods of time and at various temperatures. After treatment the samples were washed, dried and weighed. The increase in weight of the samples was noted and the samples were subjected to the match test described by J. D. Reid in the Textile Research Journal, vol. 26, page 137 (1956). None of the samples passed the match test but they showed somewhat better flame resistance than untreated cellulose. Furthermore, all of the samples were materially weakened or tenderized. However, none of the samples exhibited any after-glow whatever upon burning or charring thereof.

The results obtained in treating the materials as described are indicated in the following table.

Various samples of cellulosic fabrics were first mercerized in a 20% aqueous solution of sodium hydroxide for a period of 15 minutes. They were then washed free of excess alkali and given an acetic acid sour followed by further washing. The samples were then partially dried at 50 C. and immersed in pyridine to replace the residual water. A mesylating solution was prepared by the addition of methane sulfonyl chloride to pyridine in a quantity such that the solution contained 3 moles of the methane sulfonyl chloride for each mole of the cellulosic fabric (based on the molecular weight of 162 for the cellulose monomer). The samples were immersed in the mesylating solution and were preheated to 65 C. fora period of 10 minutes. They were then removed, washed thoroughly with soap, and dried. The resulting mesylated fabric was then again wetted out with water and dried in 50 C. after which the residual water was replaced by soaking in pyridine. The samples were then immersed in pyridine to which had been added diethyl chlorophosphate in amount sufficient to give 3 moles of the diethyl chlorophosphate to 1 mole of cellulose. The reaction was allowed to proceed at room temperature for various periods of time after which the samples were removed, washed, dried and weighed. No tenderizing of the fabric occurred. When subjected to the match test the products again failed but exhibited no after-glow whatever. The flame resistance was however greater than that of the untreated material.

The results thereby obtained are indicated in the following table EXAMPLE HI The process of Example I was carried out while further adding mesyl chloride to the pyridine along with the diethyl chlorophosphate, whereby a product was obtained which showed increased flame resistance and no afterglow. This product is mesyl phosphocellulose.

The characteristic resistance to after-glow of the products of the present invention is persistent in that even when the charred material was subjected to prolonged heating in the flame of a Bunsen burner, no after-glow resulted, indicating that no loss of phosphorus occurs during the burning of the material.

In order to render the material both flame resistant and to prevent after-glow, the cellulose may be subjected to treatment in accordance with our copending application referred to above, to esterify the hydroxyl group in the 6 position of the glucose anhydride unit by mesylation. Further, some of the mesyloxy groups may be replaced by halogens such as bromine or iodine whereby a product is obtained which is highly resistant to burning and exhibits no after-glow whatever. The esterification reaction can be carried on either simultaneously with, or before, or after the phosphorylation of the cellulose.

EXAMPLE IV The mesyl phosphocellulose of the proceeding example was treated with an aqueous solution of sodium bromide and the material refluxed for a period of 3 hours. Solid barium carbonate was added to the mixture to remove any acid liberated and to maintain the pH value of the reaction mixture about 7. The fabric was then removed, washed and dried and was found to possess excellent flame resistant properties without any after-glow, even upon prolonged heating in the flame of a Bunsen burner.

EXAMPLE V Mesyl-6-halo cellulose produced in accordance with our copending application was phosphorylated in pyridine by means of diethyl chlorophosphate, thereby indicating that the phosphorylation can be effected before, during or after esterification and substitution in the 6 position of the glucose anhydride unit.

EXAMPLE VI The process of Example II was repeated and after completion thereof the dried, mesylated and phosphorylated material was immersed in an aqueous solution containing of sodium iodide. The material was heated to refluxing temperature for about 3 hours in a steam bath and sufiicient barium carbonate was added to main tain the pH value of the solution about 7. Thereafter the resulting mesyl-phospho 6 iodo-cellulose was removed, dried and subjected to the match test. All of the samples passed the match test and showed no after-glow whatever. Furthermore, none of the samples were appreciably decreased in their tensile strength. The results obtained are indicated in the following table.

Table II Reaction Percent Match Glow Re- Descrlptlon Tlme Wt. Inc. Test slstance (mlusJ 5 3.9 Passed.. Excellent. 4 1.0 .-.do. Do. 4 1.3 do..... Do. 6 5.2 do.... Do. 3.6-oz.rayo 5 2.1 .do...- Do. Do 5 0.7 .do Do.

The weight increase indicated in the foregoing table is that due to phosphorylation only and results from the presence of the diethylphosphonyl group having a molec-' ular weight of 137. The phosphorous itself represents only about one-fourth this weight and there-fore may be less than 0.2% or as high as 2% or more based on the weight of the material treated.

EXAMPLE VII Table IV Percent Halogen Char. After Sample Net Wt. Derlv L. glow Inc. (In) 3.6-0z. viscose rayon (challis). Bromo. 2. 5 None. 6oz. cotton 29. 5 Bromo. 2. 75 Do.

D 20 Bromo. 3. 25 Do.

15 Bromo. 3. 25 Do.

20 Bromo 2v 8 Do. 32 Iodo. 1. 75 D0,.

22 Iodo--. 1.9 Do.

17 Iodo 2.25 D0.

8.0 Bromo.. 2. Do.

22.5 Iodo.. 3.1 Do.

8.1 Bromo-. 2. 5 Do.

Do 10. 9 Iodo 1.75 Do. 9-02. sateen 12. 3 Bromo. 3. 25 Do. 6-oz. cotton 10.8 Iodo. 2. 25 Do.

It will appear from the results thus obtained that fabrics can be made permanently flame and glow resistant Wth an increase of weight which is no more than about 15%, whereas products heretofore treated with added agents adhering to the fabric generally have been increased in Weight by from 20 to or more in order to develop comparable flame resistant properties. Moreover, the products of the present invention, because of their change in chemical composition, do not deteriorate or lose their flame resisting and afterglow suppressing properties when laundered with either soap or detergents. The products also can be subjected to other textile treating processes and thus may be bleached, dyed or finished by conventional processes.

The phosphorylated cellulose of the present invention can, of course, be subjected to other and conventional types of flame retarding treatment by the addition of agents thereto if desired. In this way, it is possible to employ flame retarding agents which have heretofore been unsuitable because of their retained after-glow since the after-glow is eliminated by the use of the phosphorylated cellulose as a base material. The products when burned develop a carbonaceous residue but no after-glow is produced even when subjected to continued ignition in the flame of a Bunsen burner.

The agents used in pretreating the cellulose prior to phosphorylation may be varied and when employing organic sulfonyl chlorides, ethyl sulfonyl chloride, methyl sulfonyl chloride, isopropyl sulfonyl chloride, phenyl sulfonyl chloride, benzyl sulfonyl chloride, and the like may be used.

The mercerizing of the cellulose may be carried out as described but other or conventional mercerizing processes may be used.

Any water soluble halogen salt may be used in carrying out the process as exemplified by sodium fluoride, sodium chloride, sodium bromide, sodium iodide or the corresponding potassium or ammonium salts. In general, the bromine and iodine salts are preferred since the bromoand iodo-cellulose derivatives have greater flame resistance than the fluoroand chloro-derivatives. The aqueous solution employed preferably has a pH value of about 7, but may vary from about pH to pH 9 and may be controlled by the addition of: a suitable buffering agent such as barium carbonate or other alkali or alkaline-earth carbonates.

The introduction of the halogen into the cellulose molecule is preferably effected subsequent to the phosphorylating treatment but the order to the process steps may be varied. Thus the cellulose may first be mesylated and then halogenated before the phosphorylation. The esterification and halogenation can be effected simultaneously by the use of agents such as pbromobenzenesulfonyl chloride or the like and all three steps of the process can be carried out simultaneously by the use of the latter type of reagent and a phosphorylating agent in a single reaction medium.

While the material treated in each of the foregoing examples was textile fabric, the process can be carried out in treating unwoven cotton fibers or when treating paper, paper making fibers, cotton linters, viscose rayon, cuprammonium rayon and substantially any cellulose material, as well as fabrics which contain mixtures of cotton with other types of fibers. The particular reagents employed in any process and the duration and temperature of treatment can, of course, be varied to meet the conditions encountered.

In view thereof, it should be understood that the particular compositions and methods of procedure described above are intended to be illustrative only and are not intended to limit the scope of the invention.

We claim:

1. The method which comprises reacting mesyl-cellulose with a lower dialkyl phosphorus chloride in pyridine solution at a temperature below about 40 C. for a period of from. about 1 minute to 1 hour.

2. The method which comprises reacting mesyl-cellulose With a lower dialkyl phosphorus chloride in pyridine solution at a temperature below about 40 C. for a period of from about 1 minute to 1 hour, and thereafter heating the resulting product in an aqueous solution of a water soluble halide while maintaining the pH of said solution in the range pH 5 to 9.

3. The method of phosphorylating mesyl-cellulose which comprises the step of immersing the mesyl-cellulose in a pyridine solution containing from about 1 to 4 moles of a lower dialkyl halophosphate to 1 mole of the cellulose (based on a molecular weight of 162 for the glucose anhydride unit) for a period of from about 1 minute to 1 hour and at a temperature below about 40 C.

4. The method of producing a flame and glow resistant cellulose derivative wbich comprises the steps of immersing mesyl-cellulose in a pyridine solution containing from about 1 to 4 moles of a lower dialkyl halophosphate to 1 mole of the cellulose (based on a molecular weight of 162. for the glucose anhydride unit) for a period of from about 1 minute to 1 hour and at a temperature below about 40 C., and thereafter heating the resulting product in an aqueous solution of a water soluble halide while maintaining the pH of said solution in the range pH 5 to 9.

5. A cellulose derivative containing mesyl and dialkyl phosphonyl groups, said derivative embodying a plurality of glucose anhydride units which may be represented by the group CHnOR 1 OR H I l at (m wherein the Rs in said units are selected from the group consisting of mesyl, dialkyl phosphonyl and hydrogen.

6. A 6-halo cellulose derivative containing mesyl and dialkyl phosphonyl groups, said derivative embodying a plurality of glucose anhydride units which may be represented by the group wherein the Rs are selected from the group consisting of hydrogen and dialkyl phosphonyl groups.

References Cited in the file of this patent UNITED STATES PATENTS 2,033,787 Rigby Mar. 10, 1936 2,138,778 Rigby Nov. 29, 1938 2,401,440 Thomas June 4, 1946 2,678,309 Gorder et al. May 11, 1954 2,678,330 Gorder et a1. May 11, 1954 2,743,232 Chance Apr. 24, 1956 OTHER REFERENCES Pigman et al.: Chemistry of the Carbohydrates, 1948, Academic Press Inc., Publ, N.Y.C., pp. 170, 262, 389, 549, 554, 593. 

2. THE METHOD WHICH COMPRISES REACTING MESYL-CELLULOSE WITH A LOWER DIALKYL PHOSPHORUS CHLORIDE IN PYRIDINE SOLUTION AT A TEMPERATURE BELOW ABOUT 40* C. FOR A PERIOD OF FROM ABOUT 1 MINUTE TO 1 HOUR, AND THEREAFTER HEATING THE RESULTING PRODUCT IN AN AQUEOUS SOLUTION OF A WATER SOLUBLE HALIDE WHILE MAINTAINING THE PH OF SAID SOLUTION IN THE RANGE PH 5 TO
 9. 